The Coordinated Multi-Point (CoMP) transmission is considered to be an important technology in the LET-A, the application of which can expand a range of high speed transmission area in a cell, effectively improve throughput of cell-edge users and appropriately improve overall throughput of the system. As compared with a traditional case in which an user terminal is served only by one transmission node (a base station or other entity having a function of data transmission and reception), the Coordinated Multi-Point transmission is capable of providing simultaneously services of both control and data transmission to the user terminal through dynamic collaboration and coordination among multiple transmission nodes which are separated physically.
Currently, there are mainly two Coordinated Multi-Point transmission modes: Joint Processing (JP) and Coordinated Scheduling/Beamforming (CS/CB). The Joint Processing means that the data to be transmitted exists at each transmission node and may be further divided into Joint Transmission (JT) and Dynamic Cell Selection (DCS). Joint Transmission refers to transmitting Physical Downlink Shared Channel (PDSCH) from multiple transmission nodes simultaneously at the same time instant, which means that the data to the same terminal is transmitted from multiple transmission nodes simultaneously so as to improve signal quality of received data or eliminate interference from other terminals. Dynamic Cell Selection refers to transmitting PDSCH only from one transmission node at the same time instant. Coordinated Scheduling/Beamforming means that data only exists in a service cell, but the user's decision of scheduling and beamforming is determined depending on relevant information of all the cells within the cooperating set collectively.
As can be seen from above, there will exist a cooperating set both for the Joint Processing and the Coordinated Scheduling/Beamforming. Particularly, in case of Joint Processing, the cooperating set refers to a set of transmission nodes directly or indirectly involved in data transmission (in case of the data transmission mode of Dynamic Cell Selection, data transmission is dynamically accomplished by multiple transmission nodes collaboratively although only one transmission node performs data transmission each time). In case of Coordinated Scheduling/Beamforming, the cooperating set refers to a set of cells sharing the decision of scheduling and beamforming for that cell. In theory, the larger the cooperating set is, the higher the resulting performance gain is. However, from the viewpoint of cost performance, the larger the cooperating set is, the greater the amount of data required to be transmitted among cooperating sets is, and especially for the transmission mode of Joint Processing, not only control information among cells but also a large amount of data to be transmitted need to be transferred among cooperating sets. Thus, if a physical link with high capacity and low delay is not utilized among cooperating sets, then data transmission delay among cooperating sets will be resulted therefrom, thus affecting timeliness and effectiveness of Coordinated Multi-Point transmission decision and further affecting performance. It can be seen that how to appropriately select the cooperating set is a problem that has to be solved.